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8-channel LED backlight driver enables better TV screen

Posted: 12 Jul 2013 ?? ?Print Version ?Bookmark and Share

Keywords:LED backlight driver? LCD TV? FETs?

iWatt Inc. has introduced its 8-channel LED backlight driver aimed to deliver better screen performance and lower cost in next-generation 2D and 3D LCD TVs. According to the company, the iW7019 gives designers a rich set of integrated features to improve picture quality and render a more lifelike viewer experience. These include both head and tail-mode PWM dimming to reduce motion blur, and high-resolution, 12bit local dimming to improve contrast ratio.

The iW7019 integrates a DC-to-DC boost controller with 10V gate drive, high-voltage current sinks and iWatt's patented BroadLED digital current regulation technology that eliminates the need for costly LED binning, indicated the firm.

iWatt said the rich features of the iW7019 make it an ideal choice for edge-lit, direct-lit and segment-edge-lit LED LCD TV designs. It drives up to eight parallel LED strings at 85V (maximum) per channel and can sink up to 200mA per string for 2D and 450mA per string for 3D TV applications. A wide, 9-28V input supply voltage range makes the iW7019 compatible with existing TV power systems, so there is no added expense for a separate voltage rail, indicated iWatt. Comprehensive dimming modes provide maximum flexibility to support both patterned retarder and shutter glass 3D TV technologies, as well as 2D TV with just one IC.

iWatt's BroadLED digital technology claims to lower system costs by reducing the voltage offset (Vf) between mismatched LED strings. Backlight driver ICs need to drive multiple strings of LEDs, however, each LED has a different forward voltage. This voltage offset has traditionally been managed by "binning," where LEDs are sorted for similar forward voltages, but this adds significant cost. BroadLED technology senses the voltage mismatch between the multiple LED strings and adjusts each string's Vf as needed, enabling the use of loosely binned LEDs to reduce system costs. The difference in string voltages also produces higher power dissipation. BroadLED technology eliminates up to 90 per cent of this wasted power, while maintaining 2 per cent current matching, ST stated.

In addition to BroadLED technology, the iW7019 incorporates a number of additional features to reduce system costs. The integrated DC-to-DC boost controller provides a 10V gate drive, enabling the use of lower-cost power FETs, while the integrated, high-voltage current sinks eliminate the added cost of external high-voltage FETs. An on-chip frequency synthesiser lowers cost by relaxing the timing accuracy requirements on the video system timing controller. The digital control engine in the iW7019 generates the PWM wave form, manages all fault readouts and reports faults, removing the need for expensive MCUs. Additional savings come from the 85V capability on drain sensing, which eliminates external diodes usually required for LED short-circuit fault management, as well as cascodes or zener clamps typically required for protection.

The iW7019 provides comprehensive and flexible dimming modes, including 16bit SPI for high-bandwidth PWM local dimming, single direct PWM dimming with configurable phase shift, 8bit analogue dimming and hybrid dimming. The PWM dimming range is 0-100 per cent, with 12bit resolution. Precise control of the PWM output position and the PWM duty cycle offer the flexibility to support both PR and SG 3D technologies, while hybrid dimming lets users mix PWM and analogue dimming modes to maximise system efficiency. Phase-shift dimming allows the use of smaller output capacitors, eliminating audible noise, improving EMI and lowering cost.

The PLL engine on the iW7019 reduces both motion blur and waterfall noise by synchronising PWM dimming to the video signal (Vsync), supporting both head- and tail-mode dimming. Individual brightness control of each LED string facilitates local dimming, where dark areas of the display can be dimmed or turned off to improve contrast ratio.

Comprehensive, built-in protection features include over-voltage, over-current and UVLO protection on the boost controller, with open/short fault protection, and over-temperature shutdown for the LED drivers. LED short level fault detection is resistor-programmable via a single pin at four levels: 3V, 6V, 9V, 12V. When a fault is validated, the iW7019 can be programmed to turn off the entire IC or just the LED string associated with the fault.

The iW7019 comes in a 44-pin thin QFP package with an exposed die pad and supports 200mA per channel within a 50C temperature rise. It is also available in a 32pin SOP that supports 175mA per channel within a 50C temperature rise. The pin-outs for both packages are optimised for single-layer PCB layout.

The iW7019 LED driver is available in production quantities and is priced at $1.80 in 1,000-piece quantities, for either the 44-lead TQFP or 32-lead SOP package.

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